World number 12 Juan Monaco's final Australian Open preparations are in doubt after the Argentine withdrew from the invitational Kooyong tournament in Melbourne with a hand injury.

"I had a phone call from Juan Monaco's management this morning which indicated to me that he had a hand injury," tournament director Colin Stubs said.

"They're not certain how serious it is but he has been advised by his doctor not to play in the next few days with the hope that he can take his place in the Australian Open."

The Argentine's spot in the eight-man tournament, which starts on Wednesday, was taken by Paul-Henri Mathieu, Stubs said.

World number 19 Kei Nishikori also said at the club in a leafy suburb close to Melbourne's central city the knee injury that forced him out of the semi-finals in Brisbane on Saturday was still causing him problems and he did not know if he would play at Kooyong.

"I don't know," he said when asked if whether he could play.

"I'm going to try to hit today and let's see how it goes.

"It's not bad. Let's cross the fingers and hopefully it will be okay."